A signal transmission includes a first transmission device that includes: a first output amplifier that outputs a first output signal; and a first impedance circuit that has one or a plurality of reactance element provided between the first output amplifier and a transmission line, where impedance of the first impedance circuit corresponds to frequencies belonging to a first band, and is smaller than impedance corresponding to frequencies outside the first band; and a second transmission device that includes: a second output amplifier that outputs a second output signal; and a second impedance circuit that has one or a plurality of reactance elements provided between the second output amplifier and the transmission line, where impedance of the second impedance circuit corresponds to frequencies belonging to a second band differing from the first band, and is smaller than impedance corresponding to frequencies outside the second band.